Hello Richard,
not sure about NAM.
for 802.1 Q in Q on the service provider side you can force tagging of native vlan.
the only reason to use ISL in this context is that missing the native vlan concept you avoid the risk to expose the inner customer vlan tag.
forcing native vlan tagging allows to use 802.1Q external tags without this risk.
I would look at 12.2(33)SXI relase notes for suggestions.
you can find it (huge wen page..)
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/release/notes/ol_14271.html
I've found
CSCsu75546
but it is about span to NAM from port channel
CSCsv75511 applies to a NAM in standby chassis in a VSS pair
CSCsq85139 again in VSS
CSCso46210 again in VSS
CSCsk81396 : very important possible crash in 12.2(18)SXf
fixed in 12.2(18)SXF12
this has to be verified
CSCsk24272: as the one above to be verified fixed in 12.2(18)SXF12
CSCsd75273: cisco NAM vulnerability
solved in 12.2(18)SXF5
CSCse52951: as the one above
CSCsi11382: diag failures of NAM
solved in 12.2(33)SXH
I don't see a known bug related to QinQ and NAM module
Hope to help
Giuseppe